The present invention relates to densitometers for the measurement of the doppler shift in photographically recorded astronomical spectra as an indication of radial velocity of a celestial object's motion.
There exists a large collection of photographic plates dating from the early part of the century in which the spectrum of a star is recorded between two reference spectra, such as that for iron. The plate is analyzed for an indication of the shift in the location of certain spectral features known to exist in celestial spectra, such as hydrogen absorption lines, relative to the position of emission lines or signatures characteristic of the reference spectra. This shift identifies the doppler shift in the stellar track and thus the radial velocity of the body being recorded. In order to determine this shift in the past it has been necessary to scan each track separately to produce a digitized or other representation of each spectrum with some form of positional reference so that the adjacent spectra can be later compared. The multiple scan technique introduced registration errors between the scans and admitted of inaccuracies in the determination of the body's doppler shift.
In addition, the equipment used in the past to scan the tracks was expensive due at least in part to the use of expensive photomultiplier tubes, optical encoders and two dimensional positioning capabilities. Because of the multiple scan technique utilized, added cost was required to achieve precise equipment that would minimize the scan to scan registration errors. The slowness of the prior equipment and its high cost, has kept the vast number of photographic plates from being scanned to any significant degree. This is very unfortunate because the record provided by these plates, extending so far back in time, could provide important information to the astronomical world.
Other technologies can also profit from the presence of equipment capable of high speed and accurate scanning of adjacent reference and specimen spectra. One example includes the field of chromotagraphy where, for example, automated comparison of stained protein jell electrophoresis samples with standards would increase the efficiency of analysis. In molecular biological research on the quantization of DNA sequence copy number or RNA transcript number is dependent upon obtaining accurate autoradiographic signals and comparing them with a known dilution series of appropriate standards.